A quick Google search shows that most commercial usenet providers do not have more then 3000 days worth of text retention. (ie, you can get a little more then 8 years worth of history).

* Altopia has 499 days of text retention (https://www.altopia.com/retention/retention.html)

* NewsDaemon has 720 days of text retention (http://www.newsdemon.com/newsgroup-retention.php)

* Giganews has ~ 960 days of text retention (http://www.giganews.com/news/article/retention_grows.html)

So, unless someone out there has terabytes worth of text storage from way back when (which is one reason why Google bought Deja News in the first place), I don't think it will be possible to get all that history.